As a typical example of a display device, a liquid crystal display device and an organic EL (electroluminescence) display device respectively having a liquid crystal element and a light-emitting element in each pixel are represented. These display devices have a liquid crystal element or an organic light-emitting element (hereinafter, referred to as a light-emitting element) in each of a plurality of pixels formed over a substrate. A liquid crystal element and a light-emitting element respectively possess a liquid crystal and a layer (hereinafter, referred to as an organic EL layer) including an organic compound between a pair of electrodes and are driven by applying a voltage or supplying a current to the pair of electrodes.
Apart from the case of a liquid crystal element, since a light-emitting element is formed as an all-solid display element, even if the substrates are provided with flexibility and folded or bent, variation of a gap between the substrates does not cause any influence. Therefore, display quality is not influenced in principle. Thus, a so-called flexible display (sheet display) in which a light-emitting element is formed over a flexible substrate has been fabricated. For example, a bendable flexible organic EL display device is disclosed in Japanese patent application publications No. 2015-72362 and 2014-182306.